As President Biden approaches the one-year mark of his tenure in office, hundreds of key roles across the federal government remain vacant, due to a lengthening confirmation process and a greater willingness by presidents to rely on acting officials in the government.

Since 1960, the number of Senate-confirmed positions across the federal government has grown by more than 40 percent, according to an analysis from Vanderbilt University professor David Lewis and from the Partnership for Public Service.

This growth has coincided with a lengthening confirmation process, as senators have become more willing to object to individual nominees. The time that it takes to confirm a successful nominee has increased from 36 days in 1981 to 132 days in 2020, according to an analysis from the Partnership for Public Service.

Indeed, seven of President George W. Bush’s Cabinet nominees were confirmed on his first day in office in 2001, and his entire Cabinet was confirmed within his first two weeks in office. By comparison, not a single Biden Cabinet nominee was confirmed on his first day in office, and Biden did not have his full Cabinet in place until March 22.

Aside from a growing number of vacancies across the government, this lengthening process has also led to an increasing willingness of presidents to rely on acting officials to run federal agencies and implement policies. U.S. Citizenship and Immigration Services went without a Senate-confirmed director for the final 19 months of Donald Trump’s presidency; the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) has not had a Senate-confirmed director since 2015; and even the Food and Drug Administration, responsible for reviewing coronavirus vaccines and treatments, went nearly 10 months this year before Biden nominated Robert M. Califf to head the agency in November.